Electrostatic coating apparatus



Oct. 14, 1969 U A ET AL 3,472,204

ELECTROSTATIC COATING APPARATUS Filed June 14, 1968 Fig.2

/g) l J/ mvsmon NORMAN s. CURTIS Q NORBERT M. ZUPAN United States Patent3,472,204 ELECTROSTATIC COATING APPARATUS Norbert M. Zupan, Brownsburg,and Norman S. Curtis,

Indianapolis, Ind., assignors to Ransburg Electro-Coating Corp.,Indianapolis, Ind., a corporation of Indiana Continuation-impart ofapplication Ser. No. 470,152,

July 7, 1965. This application June 14, 1968, Ser.

Int. Cl. B05!) 5/08, 13/04 U.S. Cl. 118-631 6 Claims ABSTRACT OF THEDISCLOSURE The apparatus of this invention is directed toward coatingchanneled articles and other articles having depressions, recesses orother irregularities and comprises a spray gun for projecting a spray ofcoating material particles along a predetermined axis, conveyor formoving one or more channeled articles through the spray and a supportingstructure for the spray gun. The spray gun may be mounted at an acuteangle with respect to the conveyor. The spray gun supporting structureincludes means to intercept the channel of the article and to align itwith the spray axis. It also includes means which is movable from anequilibrium position and biased to return to that position and isadapted to keep the article out of contact with stationary objects as itmoves through the spray. The gun support structure may include means topermit pivotal movement so that movement of the spray gun and theintercepting means is transverse to the conveyor movement. The spray gunmay be a hydrostatic-electrostatic gun of the type shown and describedin U.S. Letters Patent 3,169,883.

This is a continuation-in-part of application Ser. No. 470,152, filedJuly 7, 1965, now abandoned.

This invention relates to an apparatus for electrostatically coatingarticles, particularly channeled or grooved articles.

Electrostatically spray coating articles of manufacture is a well knownand widely practiced art in which charged coating material particles aredeposited on an oppositely charged article. However, electrostaticallycoating some articles presents difiiculties because of the particularshape or configuration of the article. For example, articles ofmanufacture having deep grooves or deeply channeled sections, such asceiling joists and deeply corrugated metal roof decking, are moredilficult to coat electrostatically than those which are flat or haveonly shallow indentations. Unless the charged coating material particlesare given a strong mechanical push in the direction of the channel, suchas may ocur when the coating material is atomized by hydraulic pressure,compressed air or other mechanical means, the electrostatic attractionbetween the charged particles and the top portion of the side walls of adeep channel will result in satisfactory deposition of coating materialon the top portion, but little or no deposition of coating material nearthe bottom of the channel.

Electrostatic coating methods in which atomization is effected byinteraction with air, such as by compressed air or hydraulic pressure,impart a substantial directional mechanical momentum to the chargedcoating material particles so that if properly directed they may bedeposited uniformly in the depths of a channel, thus in part at leastovercoming the electrostatic attraction to the upper sides of thechannel. Because of the directional nature of the projected spray,however, alignment between the axis of the spray pattern and the axis ofthe channel is critical if satisfactory deposition in the channel is tobe achieved. Misalignment of these axes will result in non-uniform g CCdeposition in the channel. Long narrow articles are likely to move aboutconsiderably while being carried along on a conveyor into and through acoating zone. Although guide rails along the conveyor may somewhatconfine article movement, especially movement from side to side, theycannot prevent such movement and at the same time permit longitudinalmovement along the conveyor. If the channeled articles are to be coatedrapidly, the guide rails must be so spaced that the articles are free tomove. Where the spraying device is hand held by an operator, theoperator can generally direct the spray accurately toward the articleand into any channels or depressions therein, even though the articlemay move somewhat erratically. Where the spraying device is to beoperated automatically, however, the possibility of such erraticmovement of the article requires the provision of means to assure thatthe spray is properly directed toward the article and toward any channeltherein.

One embodiment of this invention includes an electrostatic spray gun inwhich coating material is supplied at a very high pressure to a smallelongated orifice to be projected therefrom into a thin fan-shaped filmat very high velocity to be atomized by interaction with air and inwhich the atomized coating material is charged by a slim elongatedelectrode adjacent said orifice. The electrostatic spray gun is mountedon a. movable support With the spray axis oriented at an acute angle tothe conveyor which carries the articles. The movable support is arrangedto have an equilibrium position that will position the channeledarticles intermediate guide rails of a conveyor. Upon being struck bythe misaligned channel of an article, the support will transiently movelaterally to intercept the channel of the article. The support willreturn to its equilibrium position with the article. By means connectedto the support, the channel of the article and the axis of the projectedspray are aligned, and alignment is maintained while the conveyor movesthe channeled article through the projected spray. The alignment meansis, of course, adjustable so that it may accommodate difierent sizes andvarious types of channeled articles.

Various features and advantages will be apparent from the descriptionand drawings in which:

FIG. 1 is a side elevational view of one form of apparatus embodyingthis invention; and FIG. 2 is an end elevational view of the apparatusshown in FIG. 1.

Referring now to FIG. 1, a support 10 pivotally mounted at 11 ispositioned opposite a conveyor 12 which includes a series ofpower-driven rollers 13. A hydraulicelectrostatic spray gun 14, whichmay be of a type described in U. S. Patent 3,169,883, is adjustablysupported from support 10 by mounting bracket 15. Coating material issupplied to spray gun 14 by means of hydraulic pump 16 at appropriatepressures. The coating material is emitted through a small elongatedorifice 17 (shown in FIG. 2), formed into an expanding fan-like spraywhich is directed generally along the axis of the spray gun. Highvoltage is brought to the spray gun from high voltage source 18 throughhigh voltage cable 20 which passes through the insulating body of thegun to a slender elongated electrode 19 positioned closely adjacent butspaced from orifice 17 so as to charge the spray particles. Typically,such an electrostatic spray gun incorporates a resistor of severalhundred megohms between the electrode and the high voltage source, andthe high voltage source has an output voltage of about 60 kilovolts.

Mounting bracket 15 orients spray gun 14 so that the axis of directionof emission of the charged spray particles lies at an acute angle withrespect to the plane of the conveyor. Two bars 21 are mounted on support10 and carry centrally between them a fork-like member 22 having legs22a and 22b. Fork-like member 22 is aligned with the axis of the spraygun and is rotatable about a shaft 23 which extends between bars 21. Aseries of points 22c are provided about which the fork-like member mayrotate to accommodate different articles. A guiding roller 24 isjournaled on a shaft 25 between legs 22a and 22b. Guiding roller 24 hasa tapered periphery 29 which will fit in the channel of the articles andby bearing on the sides of the channel will align the channel and theaxis of the spray emitted from the spray gun 14. At the rear end ofmember 22, biasing means, such as spring 26, supported from support 10,provides sufficient pressure to cause the periphery 29 of guiding roller24 to maintain contact with the channel of the article 27. Elements 10,15, 21, 22, 23, 24, and 25 make up the supporting structure of the spraygun. Various sizes and shapes of rollers can be used, depending on theparticular article being coated.

Pivot mounting 11 is centered above the conveyor 12 and between guiderails 28. The spray gun 14 and its supporting structure including thearticle guiding roller 24,

hang in an equilibrium position that is centered between L the guiderails and is free to swing transversely of the direction of articlemovement.

In operation a channeled article, such as a hat-section ceiling joist27, is moved horizontally along conveyor 12 from left to right as shownin FIG. 1. Guide rails 28 guide the article 27 so that the channel maybe engaged by guiding roller 24. If the channel of the article is notaligned With the guiding roller 24, pivot mounting 11 will permit thesupport to swing, transiently moving the guiding roller 24 and the spraygun laterally to intercept the article. The pendulum action of the spraygun and its supporting structure bias it to return to its equilibriumposition and to move the article to a position out of contact with thestationary guide rails of the conveyor, permitting articles to berapidly conveyed through the coating zone. By means of spring 2 6,sufficient pressure is exerted on fork 22 to maintain guiding roller 24in contact with the channel 27a in article 27. As the article is movedalong the conveyor and through the coating zone at the intersection ofthe atomized spray and the conveyor, alignment is automaticallymaintained between the axis of the channel 27a in article 27 and theaxis of the direction of the spray emitted from the spray gun 14. Wherea plurality of such articles are to be coated, they may be conveyed endto end through the coating zone so that the guiding roller will bridgethe interface between the ends. Typical coating material such as redoxide primer thinned to 20 seconds, Zahn 2 with xylol is supplied at 920pounds per square inch fluid pressure to an orifice having an areaequivalent that of a circle .015 of an inch in diameter and forming anexpanding fan-like spray having an included angle of The orifice ispositioned approximately three inches from the top surface of thehat-shaped section and the spray was projected downwardly at an angle ofwith respect to horizontal. Approximately 12 to 15 inches exist betweenthe point of guidance and the coating zone. This hat-shaped section hada channel 2%. inches wide and 1% inches deep. With the hat-shapedsection carried through the coating zone at the rate of 125 feet perminute a uniform coating of /2 mil of primer was achieved on the entiresurface of the channel even though the center line of the channelwobbled about 1 /2 inches.

Channeled articles of varying heights may also be coated by mounting thesupport 10 on a reciprocator whose vertical position is controlled bythe height of the channeled article being presented to the coating zone.

Although the invention is described and shown with a source of spray inwhich atomization is effected by using very high fluid supply pressuresand a small orifice, it is apparent that the invention is equallyadvantageous with a source of spray in which atomization is efiected byusing compressed air.

We claim:

1. Apparatus for coating channeled articles comprising, a spray gun toproject a spray of coating material particles along an axis, a conveyorto move channeled articles through said spray, and a supportingstructure for said spray gun including means to intercept the channel ofthe article and to align it with the axis of the spray, said supportingstructure being movable from an equilibrium position and biased toreturn to that position and to keep the article out of contact withstationary objects as it moves through the spray.

2. Apparatus for electrostatically coating an article with a channel,comprising a pivotable support, an electrostatic spray gun mounted onthe support and having an elongated orifice and a charging electrodeadjacent to said orifice, means for supplying coating material to saidorifice at very high pressures, means for charging said electrode, aconveyor to move the article past said spray gun, a guiding rollermounted on the support aligned with the axis of the spray gun, andshaped to engage the channel of the article to maintain the alignmentbetween the channel and the axis of the spray gun as the article movespast the spray gun, said pivotable support permitting movement of thespray gun and guiding roller transverse to the conveyor movement.

3. Apparatus as set forth in claim 2 wherein said atomizer is mounted atan acute angle with respect to the conveyor.

4. Apparatus for electrostatically coating a channeled article,comprising a pivot, a support movably carried by said pivot, anelectrostatic spray gun for mechanically atomizing coating materialmounted to said support, a pair of bars mounted to said support, afork-like member rotatable about a shaft extending between said bars, aguiding roller journaled between the legs of said forklike member andhaving a periphery shaped to engage the channel of said article, andbias means acting on said fork-like member to maintain the engagement ofthe guiding roller with the channel of the article.

5. Apparatus as set forth in claim 4 wherein a conveyor supports thearticle and moves it horizontally past the spray gun, the pivot permitsthe support to swing transversely to the direction of article movementand the fork-like member includes a series of points about which it isrotatable to permit accommodation of dilferent articles.

6. Apparatus for electrostatically coating a channeled articlecomprising, an atomizer to atomize and mechanically impart a momentum toa spray of coating material, an electrode to charge the spray and createan electrostatic depositing field, a conveyor to move the channeledarticles through the charged spray, and means aligned with the axis ofthe spray to maintain the alignment of the axis of the channel with theaxis of the spray during deposition of the spray.

References Cited UNITED STATES PATENTS 1,419,686 6/ 1922 Nicholson118-307 1,960,725 5/1934 Bramsen et al. 118-307 2,015,768 10/1935Thomson 118-208 2,782,757 2/1957 Carnes 118-305 XR 2,904,894 9/ 1959Hurst 118-8 XR 3,162,886 12/1964 Wise 118-307 XR 3,253,782 5/1966Fischer et al. 117-934 XR 3,342,158 9/1967 Bennet et al. 118-7 PETERFELDMAN, Primary Examiner U.S. Cl. X.R. 117-93.4, 96; 118-307

